Quantum Dot Based Color Conversion Layer in Display Devices

ABSTRACT

Embodiments of a display device including barrier layer coated quantum dots and a method of making the barrier layer coated quantum dots are described. Each of the barrier layer coated quantum dots includes a core-shell structure and a hydrophobic barrier layer disposed on the core-shell structure. The hydrophobic barrier layer is configured to provide a distance between the core-shell structure of one of the quantum dots with the core-shell structures of other quantum dots that are in substantial contact with the one of the quantum dots. The method for making the barrier layer coated quantum dots includes forming reverse micro-micelles using surfactants and incorporating quantum dots into the reverse micro-micelles. The method further includes individually coating the incorporated quantum dots with a barrier layer and isolating the barrier layer coated quantum dots with the surfactants of the reverse micro-micelles disposed on the barrier layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Appl. No.62/262,241, filed Dec. 2, 2015, and is incorporated by reference hereinin its entirety.

BACKGROUND OF THE INVENTION Field

The present invention relates to display devices including highlyluminescent quantum dots (QDs) comprising a core-shell structure.

Background

Quantum dots (QDs) have the unique ability to emit light at a singlespectral peak with narrow line width, creating highly saturated colors.It is possible to tune the emission wavelength based on the size of theQDs. This ability to tune the emission wavelength enables displayengineers to custom engineer a spectrum of light to maximize both theefficiency and color performance of the display.

The size-dependent properties of QDs are used to produce a QD film. TheQD film may be used as a color down conversion layer in display devices.The use of a color down conversion layer in emissive displays canimprove the system efficiency by down-converting white light to a morereddish light, greenish light, or both before the light passes through acolor filter. This use of a color down conversion layer may reduce lossof light energy due to filtering.

QDs may be used as the conversion material due to their broad absorptionand narrow emission spectra. Because, the density of QDs required forsuch application is very high in a very thin color down conversion layerof about 3 μm-6 μm, QDs prepared using current methods suffer fromquenching of their optical properties when the QDs are closely packednext to each other in a thin QD film. As such, current QD-based displaydevices using QD films as color down conversion layers suffer from lowquantum yield (QY).

SUMMARY

Accordingly, there is need to increase the quality of display devices.Disclosed herein are embodiments that overcome the above mentionedlimitations of display devices.

According to an embodiment, a method of making barrier layer coatedquantum dots includes forming a solution of reverse micro-micelles usingsurfactants and incorporating quantum dots into the reversemicro-micelles. The method further includes individually coating thequantum dots with a barrier layer to form barrier layer coated quantumdots and isolating the barrier layer coated quantum dots with thesurfactants of the reverse micro-micelles disposed on the barrier layer.

According to an embodiment, the incorporating of the quantum dots intothe reverse micro-micelles includes forming a first mixture of thequantum dots and the solution of reverse micelles.

According to an embodiment, the individually coating of the quantum dotswith a barrier layer includes forming a second mixture of a precursorand the first mixture and forming a third mixture of a catalyst and thesecond mixture.

According to an embodiment, the isolating of the barrier layer coatedquantum dots includes heating the third mixture at or below atemperature of about 50° C. under vacuum.

According to an embodiment, the barrier layer coated quantum dotsexhibit a quantum yield greater than about 80%.

According to an embodiment, the barrier layer coated quantum dotsexhibit a quantum yield greater than about 90%.

According to an embodiment, the barrier layer coated quantum dotsexhibit a quantum yield in a range of about 85% to about 95%.

According to an embodiment, the quantum dots and the barrier layercoated quantum dots exhibit a quantum yield greater than about 80%.

According to an embodiment, the quantum dots and the barrier layercoated quantum dots exhibit a quantum yield greater than about 85%.

According to an embodiment, the barrier layer coated quantum dots havean average size ranging from about 20 nm and to about 40 nm in diameter.

According to an embodiment, the barrier layer coated quantum dots havean average size ranging from about 25 nm and to about 35 nm in diameter.

According to an embodiment, the barrier layer includes an oxide.

According to an embodiment, the barrier layer includes silicon oxide.

According to an embodiment, a quantum dot film includes barrier layercoated quantum dots. Each of the barrier layer coated quantum dotsincludes a quantum dot and an optically transparent barrier layerdisposed on the quantum dot. The optically transparent barrier layer isconfigured to provide a spacing between adjacent quantum dots to preventaggregation of the adjacent quantum dots. The quantum dot film furtherincludes a matrix material configured to house the barrier layer coatedquantum dots and be in substantial contact with the opticallytransparent barrier layer. The barrier layer coated quantum dots exhibita quantum yield greater than about 80%.

According to an embodiment, the optically transparent barrier layer ishydrophobic.

According to an embodiment, the spacing is equal or greater than aForster radius between adjacent barrier layer coated quantum dots.

According to an embodiment, the quantum dot of each of the barrier layercoated quantum dots includes a core-shell structure having a core and ashell surrounding the core.

According to an embodiment, the core includes a first material, theshell includes a second material, and the optically transparent barrierlayer includes a third material. The first, second, and third materialsare different from each other.

According to an embodiment, the optically transparent barrier layerincludes an oxide.

According to an embodiment, the optically transparent barrier layerincludes silicon oxide.

According to an embodiment, the quantum dot film further includessurfactants or ligands bonded to the optically transparent barrierlayer.

According to an embodiment, the quantum dot film exhibits an externalquantum efficiency greater than about 50% after being treated at atemperature greater than 200° C.

According to an embodiment, the quantum dot film includes an opticaldensity greater than about 0.24 and an external quantum efficiencygreater than about 50%.

According to an embodiment, the barrier layer coated quantum dots havean average size ranging from about 20 nm and to about 40 nm in diameter.

According to an embodiment, the optically transparent barrier layer hasa thickness ranging from about 8 nm and to about 20 nm in diameter.

According to an embodiment, the matrix material includes an extrudablematerial.

According to an embodiment, the matrix material includes a brightnessenhancement film.

According to an embodiment, the matrix material includes a polymerplastic film.

According to an embodiment, the quantum dot film includes a thickness ina range from about 70 μm to about 40 μm.

According to an embodiment, a display device includes an organic layerthat emits a broadband radiation and a quantum dot film disposed on theorganic layer. The quantum dot film includes barrier layer coatedquantum dots that absorb a set of wavelengths of the broadband radiationand emit at a primary emission peak wavelength, where the set ofwavelengths is smaller than the primary emission peak wavelength. Eachof the barrier layer coated quantum dots includes a core-shell quantumdot and an optically transparent barrier layer surrounding thecore-shell quantum dot. The barrier layer coated quantum dots exhibit aquantum yield greater than about 80%. The quantum dot film furtherincludes a matrix material configured to house the barrier layer coatedquantum dots and be in substantial contact with the opticallytransparent barrier layer. The display device further includes anoptical element, disposed on the quantum dot film, configured to blockanother set of wavelengths of the broadband radiation that are greaterthan the primary emission peak wavelength.

According to an embodiment, the optically transparent barrier layer isconfigured to provide a spacing between adjacent barrier layer coatedquantum dot to prevent their aggregation.

According to an embodiment, the spacing is equal or greater than aForster radius between adjacent barrier layer coated quantum dots.

According to an embodiment, the organic layer, the quantum dot film, andthe optical element are part of a pixel unit of the display device.

According to an embodiment, the optical element is a color filter.

According to an embodiment, the barrier layer includes an oxide.

According to an embodiment, the quantum dot film further includessurfactants or ligands bonded to the optically transparent barrierlayer.

According to an embodiment, the optically transparent barrier layer isconfigured to protect the core-shell quantum dot from degradation bylight flux, heat, oxygen, moisture, or a combination thereof.

According to an embodiment, a light emitting diode (LED) device includesa light source unit, a quantum dot film disposed on the light sourceunit, and an optical element disposed on the quantum dot film.

According to an embodiment, a method of making the barrier layer coatedquantum dots includes forming a solution of reverse micro-micelles usingsurfactants, incorporating quantum dots into the reverse micro-micelles,individually coating the quantum dots with a barrier layer to form thebarrier layer coated quantum dots, and performing an acid etch treatmentof the barrier layer coated quantum dots.

According to an embodiment, the method further includes isolating thebarrier layer coated quantum dots with the surfactants of the reversemicro-micelles disposed on the barrier layer after the performing of theacid etch treatment.

According to an embodiment, the incorporating of the quantum dots intothe reverse micro-micelles includes forming a first mixture of thequantum dots and the solution of reverse micelles.

According to an embodiment, the individually coating of the quantum dotswith the barrier layer includes forming a second mixture of a precursorand the first mixture and forming a third mixture of a catalyst and thesecond mixture.

According to an embodiment, the performing of the acid etch treatment ofthe barrier layer quantum dots includes forming a fourth mixture of anacid and the third mixture.

According to an embodiment, the performing of the acid etch treatment ofthe barrier layer quantum dots includes selectively removing thecatalyst and forming a fourth mixture of an acid and the third mixture.

According to an embodiment, the acid includes acetic acid, hydrochloricacid, nitric acid, or a fatty acid.

According to an embodiment, a method of making a quantum dot filmincludes forming barrier layer coated quantum dots, forming a homogenousmixture of the barrier layer quantum dots and a matrix material, andperforming an extrusion process on the homogenous mixture.

According to an embodiment, the performing of the extrusion processincludes introducing the homogenous mixture into a hopper, extruding afilm having the barrier layer coated quantum dots and the matrixmaterial through a slot die, and passing the extruded film through chillrolls.

According to an embodiment, the matrix material includes an extrudablematerial.

According to an embodiment, the matrix material includes a polymerplastic film.

According to an embodiment, the quantum dot film includes a thickness ina range from about 70 μm to about 40 μm.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present embodiments and, togetherwith the description, further serve to explain the principles of thepresent embodiments and to enable a person skilled in the relevantart(s) to make and use the present embodiments.

FIG. 1 illustrates a cross-sectional structure of a barrier layer coatedQD, according to an embodiment.

FIGS. 2A-2B illustrate a process of forming core-shell QDs, according toan embodiment.

FIGS. 3A-3B illustrate transmission electron micrographs of CdSe basedQDs, according to an embodiment.

FIGS. 4A-4E illustrate example optical characteristics of CdSe basedQDs, according to an embodiment.

FIGS. 5A-5C illustrate a process of forming barrier layer coated QDs,according to an embodiment.

FIG. 6 illustrates a transmission electron micrograph of barrier layercoated QDs, according to an embodiment.

FIGS. 7A-7B illustrate example optical characteristics of barrier layercoated QDs, according to an embodiment.

FIG. 8 is a flowchart for forming oxide coated QDs, according to anembodiment.

FIG. 9 illustrates a QD film, according to an embodiment.

FIG. 9A illustrates a method of forming a QD film, according to anembodiment.

FIG. 9B illustrates a cross-sectional view of the QD film of FIG. 9,according to an embodiment.

FIG. 10 illustrates an example optical characteristics of a QD film,according to an embodiment.

FIG. 11 illustrates a cross-sectional view of a display panel of adisplay device, according to an embodiment.

FIG. 12 illustrates a schematic of an exploded cross-sectional view of aQD film based pixel unit of a display device, according to anembodiment.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number. Unless otherwise indicated, the drawings providedthroughout the disclosure should not be interpreted as to-scaledrawings.

DETAILED DESCRIPTION OF THE INVENTION

Although specific configurations and arrangements may be discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present invention. It will be apparent to aperson skilled in the pertinent art that this invention can also beemployed in a variety of other applications beyond those specificallymentioned herein.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” etc., indicate that theembodiment described may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesdo not necessarily refer to the same embodiment. Further, when aparticular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

All numbers in this description indicating amounts, ratios of materials,physical properties of materials, and/or use are to be understood asmodified by the word “about,” except as otherwise explicitly indicated.

The term “about” as used herein indicates the value of a given quantityvaries by ±10% of the value, or optionally ±5% of the value, or in someembodiments, by ±1% of the value so described. For example, “about 100nm” encompasses a range of sizes from 90 nm to 110 nm, inclusive.

The term “forming a reaction mixture” or “forming a mixture” as usedherein refers to combining at least two components in a container underconditions suitable for the components to react with one another andform a third component.

The term “nanostructure” as used herein refers to a structure having atleast one region or characteristic dimension with a dimension of lessthan about 500 nm. In some embodiments, the nanostructure has adimension of less than about 200 nm, less than about 100 nm, less thanabout 50 nm, less than about 20 nm, or less than about 10 nm. Typically,the region or characteristic dimension will be along the smallest axisof the structure. Examples of such structures include nanowires,nanorods, nanotubes, branched nanostructures, nanotetrapods, tripods,bipods, nanocrystals, nanodots, QDs, nanoparticles, and the like.Nanostructures can be, e.g., substantially crystalline, substantiallymonocrystalline, polycrystalline, amorphous, or a combination thereof.In some embodiments, each of the three dimensions of the nanostructurehas a dimension of less than about 500 nm, less than about 200 nm, lessthan about 100 nm, less than about 50 nm, less than about 20 nm, or lessthan about 10 nm.

The term “QD” or “nanocrystal” as used herein refers to nanostructuresthat are substantially monocrystalline. A nanocrystal has at least oneregion or characteristic dimension with a dimension of less than about500 nm, and down to the order of less than about 1 nm. The terms“nanocrystal,” “QD,” “nanodot,” and “dot,” are readily understood by theordinarily skilled artisan to represent like structures and are usedherein interchangeably. The present invention also encompasses the useof polycrystalline or amorphous nanocrystals.

The term “heterostructure” when used with reference to nanostructuresrefers to nanostructures characterized by at least two different and/ordistinguishable material types. Typically, one region of thenanostructure comprises a first material type, while a second region ofthe nanostructure comprises a second material type. In certainembodiments, the nanostructure comprises a core of a first material andat least one shell of a second (or third etc.) material, where thedifferent material types are distributed radially about the long axis ofa nanowire, a long axis of an arm of a branched nanowire, or the centerof a nanocrystal, for example. A shell can but need not completely coverthe adjacent materials to be considered a shell or for the nanostructureto be considered a heterostructure; for example, a nanocrystalcharacterized by a core of one material covered with small islands of asecond material is a heterostructure. In other embodiments, thedifferent material types are distributed at different locations withinthe nanostructure; e.g., along the major (long) axis of a nanowire oralong a long axis of arm of a branched nanowire. Different regionswithin a heterostructure can comprise entirely different materials, orthe different regions can comprise a base material (e.g., silicon)having different dopants or different concentrations of the same dopant.

As used herein, the term “diameter” of a nanostructure refers to thediameter of a cross-section normal to a first axis of the nanostructure,where the first axis has the greatest difference in length with respectto the second and third axes (the second and third axes are the two axeswhose lengths most nearly equal each other). The first axis is notnecessarily the longest axis of the nanostructure; e.g., for adisk-shaped nanostructure, the cross-section would be a substantiallycircular cross-section normal to the short longitudinal axis of thedisk. Where the cross-section is not circular, the diameter is theaverage of the major and minor axes of that cross-section. For anelongated or high aspect ratio nanostructure, such as a nanowire, thediameter is measured across a cross-section perpendicular to the longestaxis of the nanowire. For a spherical nanostructure, the diameter ismeasured from one side to the other through the center of the sphere.

The terms “crystalline” or “substantially crystalline,” when used withrespect to nanostructures, refer to the fact that the nanostructurestypically exhibit long-range ordering across one or more dimensions ofthe structure. It will be understood by one of skill in the art that theterm “long range ordering” will depend on the absolute size of thespecific nanostructures, as ordering for a single crystal cannot extendbeyond the boundaries of the crystal. In this case, “long-rangeordering” will mean substantial order across at least the majority ofthe dimension of the nanostructure. In some instances, a nanostructurecan bear an oxide or other coating, or can be comprised of a core and atleast one shell. In such instances it will be appreciated that theoxide, shell(s), or other coating can but need not exhibit such ordering(e.g. it can be amorphous, polycrystalline, or otherwise). In suchinstances, the phrase “crystalline,” “substantially crystalline,”“substantially monocrystalline,” or “monocrystalline” refers to thecentral core of the nanostructure (excluding the coating layers orshells). The terms “crystalline” or “substantially crystalline” as usedherein are intended to also encompass structures comprising variousdefects, stacking faults, atomic substitutions, and the like, as long asthe structure exhibits substantial long range ordering (e.g., order overat least about 80% of the length of at least one axis of thenanostructure or its core). In addition, it will be appreciated that theinterface between a core and the outside of a nanostructure or between acore and an adjacent shell or between a shell and a second adjacentshell may contain non-crystalline regions and may even be amorphous.This does not prevent the nanostructure from being crystalline orsubstantially crystalline as defined herein.

The term “monocrystalline” when used with respect to a nanostructureindicates that the nanostructure is substantially crystalline andcomprises substantially a single crystal. When used with respect to ananostructure heterostructure comprising a core and one or more shells,“monocrystalline” indicates that the core is substantially crystallineand comprises substantially a single crystal.

The term “ligand” as used herein refers to a molecule capable ofinteracting (whether weakly or strongly) with one or more faces of ananostructure, e.g., through covalent, ionic, van der Waals, or othermolecular interactions with the surface of the nanostructure.

The term “quantum yield” (QY) as used herein refers to the ratio ofphotons emitted to photons absorbed, e.g., by a nanostructure orpopulation of nanostructures. As known in the art, quantum yield istypically determined by a comparative method using well-characterizedstandard samples with known quantum yield values.

The term “primary emission peak wavelength” as used herein refers to thewavelength at which the emission spectrum exhibits the highestintensity.

The term “full width at half-maximum” (FWHM) as used herein refers to ameasure of the size distribution of QDs. The emission spectra of QDsgenerally have the shape of a Gaussian curve. The width of the Gaussiancurve is defined as the FWHM and gives an idea of the size distributionof the QDs. A smaller FWHM corresponds to a narrower size distributionof the QDs. FWHM is also dependent upon the emission wavelength maximum.

The term Forster radius used herein is also referred as Forster distancein the art.

An Example Embodiment of a Barrier Layer Coated QD Structure

FIG. 1 illustrates a cross-sectional structure of a barrier layer coatedQD 100, according to an embodiment. Barrier layer coated QD 100 includesa QD 101 and a barrier layer 106. QD 101 includes a core 102 and a shell104. Core 102 includes a semiconducting material that emits light uponabsorption of higher energies. Examples of the semiconducting materialfor core 102 include indium phosphide (InP), cadmium selenide (CdSe),zinc sulfide (ZnS), lead sulfide (PbS), indium arsenide (InAs), indiumgallium phosphide, (InGaP), cadmium zinc selenide (CdZnSe), zincselenide (ZnSe) and cadmium telluride (CdTe). Any other II-VI, III-V,tertiary, or quaternary semiconductor structures that exhibit a directband gap may be used as well. In an embodiment, core 102 may alsoinclude one or more dopants such as metals, alloys, to provide someexamples. Examples of metal dopant may include, but not limited to, zinc(Zn), Copper (Cu), aluminum (Al), platinum (Pt), chrome (Cr), tungsten(W), palladium (Pd), or a combination thereof. The presence of one ormore dopants in core 102 may improve structural and optical stabilityand QY of QD 101 compared to undoped QDs.

Core 102 may have a size of less than 20 nm in diameter, according to anembodiment. In another embodiment, core 102 may have a size betweenabout 1 nm and about 5 nm in diameter. The ability to tailor the size ofcore 102, and consequently the size of QD 101 in the nanometer rangeenables photoemission coverage in the entire optical spectrum. Ingeneral, the larger QDs emit light towards the red end of the spectrum,while smaller QDs emit light towards the blue end of the spectrum. Thiseffect arises as larger QDs have energy levels that are more closelyspaced than the smaller QDs. This allows the QD to absorb photonscontaining less energy, i.e. those closer to the red end of thespectrum.

Shell 104 surrounds core 102 and is disposed on outer surface of core102. Shell 104 may include cadmium sulfide (CdS), zinc cadmium sulfide(ZnCdS), zinc selenide sulfide (ZnSeS), and zinc sulfide (ZnS). In anembodiment, shell 104 may have a thickness 104 t, for example, one ormore monolayers. In other embodiments, shell 104 may have a thickness104 t between about 1 nm and about 5 nm. Shell 104 may be utilized tohelp reduce the lattice mismatch with core 102 and improve the QY of QD101. Shell 104 may also help to passivate and remove surface trapstates, such as dangling bonds, on core 102 to increase QY of QD 101.The presence of surface trap states may provide non-radiativerecombination centers and contribute to lowered emission efficiency ofQD 101.

In alternate embodiments, QD 101 may include a second shell disposed onshell 104, or more than two shells surrounding core 102, withoutdeparting from the spirit and scope of the present invention. In anembodiment, the second shell may be on the order of two monolayers thickand is typically, though not required, also a semiconducting material.Second shell may provide protection to core 102. Second shell materialmay be zinc sulfide (ZnS), although other materials may be used as wellwithout deviating from the scope or spirit of the invention.

Barrier layer 106 is configured to form a coating on QD 101. In anembodiment, barrier layer 106 is disposed on and in substantial contactwith outer surface 104 a of shell 104. In embodiments of QD 101 havingone or more shells, barrier layer 106 may be disposed on and insubstantial contact with the outermost shell of QD 101. In an exampleembodiment, barrier layer 106 is configured to act as a spacer betweenQD 101 and one or more QDs in, for example, a solution, a composition,and/or a film having a plurality of QDs, where the plurality of QDs maybe similar to QD 101 and/or barrier layer coated QD 100. In such QDsolutions, QD compositions, and/or QD films, barrier layer 106 may helpto prevent aggregation of QD 101 with adjacent QDs. Aggregation of QD101 with adjacent QDs may lead to increase in size of QD 101 andconsequent reduction or quenching in the optical emission properties ofthe aggregated QD (not shown) including QD 101. As discussed above,optical characteristics of QDs are size dependent, and thus increase inQD size due to aggregation leads to the quenching phenomenon, which maylead to decrease in QY of QD 101. Barrier layer 106 may also prevent QD101 from reabsorbing optical emissions from other QDs in the QDsolutions, QD compositions, and/or QD films and thus, improve the QY ofthese QD solutions, QD compositions, and/or QD films. In furtherembodiments, barrier layer 106 provides protection to QD 101 from, forexample, moisture, air, and/or harsh environments (e.g., hightemperatures and chemicals used during lithographic processing of QDsand/or during manufacturing process of QD-based devices) that mayadversely affect the structural and optical properties of QD 101.

Barrier layer 106 includes one or more materials that are amorphous,optically transparent and/or electrically inactive. Suitable barrierlayers include inorganic materials, such as, but not limited to,inorganic oxides and/or nitrides. Examples of materials for barrierlayer 106 include oxides and/or nitrides of Al, Ba, Ca, Mg, Ni, Si, Ti,or Zr, according to various embodiments. Barrier layer 106 may have athickness 106 t ranging from about 8 nm to about 15 nm in variousembodiments. In some embodiments, thickness 106 t may have a minimumvalue such that a center-to-center distance between two adjacent QDs100, for example, in a solution, composition, and/or film is equal to orgreater than a Forster radius (also referred in the art as Forsterdistance) in order to reduce or substantially eliminate resonance energytransfer and/or reabsorption of optical emission between the adjacentQDs 100, and consequently, improve QY of the adjacent QDs 100. In someembodiments, thickness 106 t may have a minimum value of between about 8nm to about 15 nm.

Forster radius refers to a center-to-center distance between twoadjacent QDs, such as QDs 100 at which resonance energy transferefficiency between these two adjacent QDs is about 50%. Having acenter-to-center distance between two adjacent QDs greater than theForster radius may decrease the resonance energy transfer efficiency andimprove the optical emission properties and QY of the adjacent QDs. Theprocess of resonance energy transfer can take place when one QD in anelectronically excited state transfers its excitation energy to a nearbyor adjacent QD. The resonance energy transfer process is a non-radiativequantum mechanical process. Thus, when the resonance energy transferoccurs from the one QD, the optical emission properties of the one QDmay be quenched and the QY of the one QD may be adversely affected.

As illustrated in FIG. 1, barrier layer coated QD 100 may additionallyor optionally include a plurality of ligands or surfactants 108,according to an embodiment. Ligands or surfactants 108 may be adsorbedor bound to an outer surface of barrier layer coated QD 100, such as onan outer surface of barrier layer 106, according to an embodiment. Theplurality of ligands or surfactants 108 may include hydrophilic or polarheads 108 a and hydrophobic or non-polar tails 108 b. The hydrophilic orpolar heads 108 a may be bound to barrier layer 106. The presence ofligands or surfactants 108 may help to separate QD 100 and/or QD 101from other QDs in, for example, a solution, a composition, and/or a filmduring their formation. If the QDs are allowed to aggregate during theirformation, the quantum efficiency of QDs such as QD 100 and/or QD 101may drop. Ligands or surfactants 108 may also be used to impart certainproperties to barrier layer coated QD 100, such as hydrophobicity toprovide miscibility in non-polar solvents, or to provide reaction sites(e.g., reverse micellar systems) for other compounds to bind.

A wide variety of ligands exist that may be used as ligands 108. In someembodiments, the ligand is a fatty acid selected from lauric acid,caproic acid, myristic acid, palmitic acid, stearic acid, and oleicacid. In some embodiments, the ligand is an organic phosphine or anorganic phosphine oxide selected from trioctylphosphine oxide (TOPO),trioctylphosphine (TOP), diphenylphosphine (DPP), triphenylphosphineoxide, and tributylphosphine oxide. In some embodiments, the ligand isan amine selected from dodecylamine, oleylamine, hexadecylamine, andoctadecylamine. In some embodiments, the ligand is trioctylphosphine(TOP). In some embodiments, the ligand is oleylamine. In someembodiments, the ligand is diphenylphosphine.

A wide variety of surfactants exist that may be used as surfactants 108.Nonionic surfactants may be used as surfactants 108 in some embodiments.Some examples of nonionic surfactants include polyoxyethylene (5)nonylphenylether (commercial name IGEPAL CO-520), polyoxyethylene (9)nonylphenylether (IGEPAL CO-630), octylphenoxy poly(ethyleneoxy)ethanol(IGEPAL CA-630), polyethylene glycol oleyl ether (Brij 93), polyethyleneglycol hexadecyl ether (Brij 52), polyethylene glycol octadecyl ether(Brij S10), polyoxyethylene (10) isooctylcyclohexyl ether (TritonX-100), and polyoxyethylene branched nonylcyclohexyl ether (TritonN-101).

Anionic surfactants may be used as surfactants 108 in some embodiments.Some examples of anionic surfactants include sodium dioctylsulfosuccinate, sodium stearate, sodium lauryl sulfate, sodiummonododecyl phosphate, sodium dodecylbenzenesulfonate, and sodiummyristyl sulfate.

In some embodiments, QDs 101 and/or 100 may be synthesized to emit lightin one or more various color ranges, such as red, orange, and/or yellowrange. In some embodiments, QDs 101 and/or 100 may be synthesized toemit light in the green and/or yellow range. In some embodiments, QDs101 and/or 100 may be synthesized emit light in the blue, indigo,violet, and/or ultra-violet range. In some embodiments, QDs 101 and/or100 may be synthesized to have a primary emission peak wavelengthbetween about 605 nm and about 650 nm, between about 510 nm and about550 nm, or between about 300 nm and about 480 nm.

QDs 101 and/or 100 may be synthesized to display a high QY. In someembodiments, QDs 101 and/or 100 may be synthesized to display a QYbetween 80% and 95% or between 85% and 90%.

Thus, according to various embodiments, QDs 100 may be synthesized suchthat the presence of barrier layer 106 on QDs 101 does not substantiallychange or quench the optical emission properties of QDs 101.

QY of QDs may be calculated using an organic dye as a reference. Forexample, rhodamine (Rh) 640 as a reference for red-emitting QDs 101and/or 100 at the 530 nm excitation wavelength, fluorescein dye as areference for green-emitting QDs 101 and/or 100 at the 440 nm excitationwavelength, 1,10-diphenylanthracene as a reference for blue-emitting QDs101 and/or 100 at the 355 nm excitation wavelength. This can be achievedusing the following equation:

$\Phi_{X} = {{\Phi_{ST}\left( \frac{{Grad}_{X}}{{Grad}_{ST}} \right)}{\left( \frac{\eta_{X}^{2}}{\eta_{ST}^{2}} \right).}}$

The subscripts ST and X denote the standard (reference dye) and thecore/shell QDs solution (test sample), respectively. Φx is the quantumyield of the core/shell QDs, and Φ_(T) is the quantum yield of thereference dye. Grad=(I/A), where I is the area under the emission peak(wavelength scale); A is the absorbance at excitation wavelength. η isthe refractive index of the reference dye or the core/shell QDs in thesolvent. See, e.g., Williams et al. (1983) “Relative fluorescencequantum yields using a computer controlled luminescence spectrometer”Analyst 108:1067. The references listed in Williams et al. are for greenand red emitting QDs.

An Example Method for Forming a Core-Shell QDs

FIGS. 2A-2B illustrates different stages of formation of QDs 201,according to an embodiment. QDs 201 may be similar to QD 101, asdescribed above. It should be noted that formation of three QDs has beenshown in FIGS. 2A-2B for illustrative purposes. However, as would beunderstood by a person of skill in the art based on the descriptionherein, the methods described below can produce any number of QDssimilar to QDs 201.

Cores formation—FIG. 2A illustrates QDs 201 after formation of cores 202and native ligands or surfactants 207, according to an embodiment. Cores202 and native ligands 207 may be similar to core 102 and ligands 108,respectively. In an embodiment, cores 202 having native ligands orsurfactants 207 attached to their outer surface may be formed using asolution-phase colloidal method. The colloidal method may includeforming a first mixture comprising one or more cation precursors, one ormore anion precursors, and a solvent. The method may further includeheating a solution of one or more ligands or surfactants at a firsttemperature and forming a second mixture by rapidly injecting the firstmixture into the heated solution of one or more ligands or surfactants,followed by heating the second mixture at a second temperature. The oneor more ligands or surfactants can be any of the ligands or surfactantsdiscussed above. In some embodiments, the first temperature is betweenabout 200° C. and about 400° C. and in some embodiments, the secondtemperature is between about 150° C. and about 350° C. The firsttemperature may be selected to be sufficient enough to induce a reactionbetween the cation precursors and the anion precursors. The cation andanion precursors may react to form nuclei of reaction products. Forexample, a cation precursor such as a cadmium precursor and an anionprecursor such as a selenium precursor may react in the heated mixtureto form CdSe nuclei.

After this initial nucleation phase, growth of cores 202 from the nucleimay occur through addition of monomers, which are present in the secondmixture, to the nuclei at the second temperature that is lower than thefirst temperature. The growth of cores 202 may be stopped by removingthe heating at the second temperature after a desired size and/or shapeis achieved. This heating process at the second temperature may lastfrom about 1 min to about 120 min. The size and/or shape of theresulting cores 202 may be controlled by manipulating, independently orin combination, parameters such as the temperature, types of precursormaterials, and ratios of ligands or surfactants to monomers, accordingto various example embodiments. The size and/or shape of the resultingcores 202 may be determined using techniques known to those of skill inthe art. In some embodiments, the size and/or shape is determined bycomparing the diameter of cores 202 before and after the addition ofmonomers. In some embodiments, the diameter of cores 202 before andafter the addition of monomers is determined by transmission electronmicroscopy (TEM).

After the growth of cores 202 to a desired size and/or shape, they canbe cooled. In some embodiments, cores 202 are cooled to roomtemperature. In some embodiments, an organic solvent is added to dilutethe second mixture comprising cores 202. In some embodiments, theorganic solvent is hexane, pentane, toluene, benzene, diethylether,acetone, ethyl acetate, dichloromethane (methylene chloride),chloroform, dimethylformamide, or N-methylpyrrolidinone. In someembodiments, the organic solvent is toluene.

In some embodiments, after the growth of cores 202 to a desired sizeand/or shape, they are isolated. In some embodiments, cores 202 areisolated by precipitating them from the solvent of the second mixture orof the diluted second mixture. In some embodiments, cores 202 areisolated by flocculation with methanol, ethanol, isopropanol, orn-butanol.

In an example of this embodiment, the cation precursors may serve as asource for the electropositive element or elements in the resultingcores 202. The cation precursor can be a group II metal (e.g., Zn, Cd,or Hg), a group III metal (e.g., Al, Ga, or In), a group IV (e.g., Ge,Sn or Pb), or a transition metal (e.g., Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,W, Mn, Tc, Re, Fe, Co, Ni, Pd, Pt, Rh, and the like) precursor,according to various example embodiments. The cation precursor canconstitute a wide range of substances, such as a metal oxide, a metalcarbonate, a metal bicarbonate, a metal sulfate, a metal sulfite, ametal phosphate, metal phosphite, a metal halide, a metal carboxylate, ametal alkoxide, a metal thiolate, a metal amide, a metal imide, a metalalkyl, a metal aryl, a metal coordination complex, a metal solvate, or ametal salt, to provide some examples.

In another example of this embodiment, the anion precursors may serve asa source for the electronegative element or elements in the resultingcores 202. The anion precursor can be selected from the element itself(oxidation state zero), covalent compounds, or ionic compounds of thegroup V elements (N, P, As, or Sb), the group VI elements (O, S, Se orTe), and the group VII elements (F, Cl, Br, or I), according to variousexample embodiments.

Examples of the ligands used in the first mixture include dodecylamine(DA), hexadecylamine (HA), octadecylamine (OA), stearic acid (SA),lauric acid (LA), hexylphosphonic acid (HPA), tetradecylphosphonic acid(TDPA), trioctylphosphine (TOP), or trioctylphosphine oxide (TOPO). Inan embodiment, the ligand and the solvent may be the same chemical usedin the first mixture. For example, long-chain fatty acids and amines andTOPO may serve both the solvent and the ligand functions.

Shelling process—The core formation process may be followed by ashelling process of QDs 201, as illustrated in FIG. 2B. FIG. 2Billustrates QDs 201 after formation of shells 204. Shells 204 may besimilar to shell 104, as described above. The process of forming shells204 around cores 202 may include suspending cores 202 in a solvent or amixture of solvents such as, but not limited to, 1-octadecene, 1-decene,1-dodecene, or tetradecane, and heating the suspension of cores 202 at athird temperature. In some embodiments, the third temperature is between100° C. and about 200° C. The shelling process may further includeforming a third mixture by adding precursors that include elements ofshells 204 at a fourth temperature. In some embodiments, the fourthtemperature is between 250° C. and about 350° C. For example, cadmiumprecursor and sulfur precursor may be used in the third mixture forforming shells 204 comprising cadmium sulfide (CdS). In an example,shells 204 include group III-V material or group II-VI material. Inanother example, elements of shells 204 may be different from elementsof cores 202. The materials of cores 202 and shells 204 may be selectedsuch that the two materials have a low lattice mismatch between them.The low lattice mismatch may allow the formation of a uniform andepitaxially grown shells 204 on the surfaces of cores 202. In thismethod of first shell formation, cores 202 may act as the nuclei, forshells 204 to grow from their surface.

The growth of shells 204 on cores 202 may be stopped by removing theheating at the fourth temperature after a desired thickness of shells204 on cores 202 is achieved. This heating process at the fourthtemperature may last from about 50 min to about 100 min. The thicknessof the resulting shells 204 may be controlled by manipulating,independently or in combination, parameters such as the temperature,types of precursor materials, and amount of precursors, according tovarious example embodiments.

After the growth of shells 204 to a desired thickness, the resultingcore-shell QDs 201 can be cooled. In some embodiments, QDs 201 arecooled to room temperature. In some embodiments, after the formation ofQDs 201, they are isolated. In some embodiments, QDs 201 are isolated byprecipitation with a solvent (e.g., ethanol) and centrifugation.

In alternate embodiments, the above QD 201 formation method may includedoping cores 202 during synthesis of cores 202. The doping process maybe performed at any stage of QD 201 formation. For example, one or moredopant precursors may be introduced with the cation precursor or theanion precursor during cores 202 synthesis process or with theprecursors during the shelling process.

The cores 202 may have one or more dopants homogeneously orheterogeneously distributed throughout the cores 202. For example,higher dopant concentration may be present at the surface of the cores202 and lower dopant concentration may be present at the center of thecores, or vice versa. In another example, the one or more dopants may bedistributed substantially uniformly over the cores 202.

According to an example of this embodiment, the one or more dopantprecursors may include any suitable doping precursors such as, but notlimited to, metal oxide (e.g., zinc oxide, magnesium oxide), metalacetate (e.g., zinc acetate, cobalt acetate), metal carbonate (e.g.,zinc carbonate, cobalt carbonate, magnesium carbonate), metalbicarbonate (e.g., zinc bicarbonate, cobalt bicarbonate, magnesiumbicarbonate), metal sulfate (e.g., zinc sulfate, magnesium sulfate,cobalt sulfate), metal sulfite (e.g., zinc sulfite, magnesium sulfite),metal phosphate (e.g., zinc phosphate, cobalt phosphate, magnesiumphosphate), metal phosphite (e.g., zinc phosphite, magnesium phosphite),metal halide (e.g., zinc halide, magnesium halide), metal carboxylate(e.g., zinc carboxylate, magnesium carboxylate), metal alkoxide (e.g.,zinc alkoxide, magnesium alkoxide), metal thiolate (e.g., zinc thiolate,magnesium thiolate), metal amide (e.g., zinc amide, magnesium amide),metal imide (e.g., zinc imide, magnesium imide), metal alkyl (e.g., zincalkyl, aluminum alkyl, magnesium alkyl), or diethyl metal (e.g., diethylzinc).

The resulting core-shell QDs 201 may have a narrow size distribution(i.e., a small FWHM) and a high QY. In some embodiments, thephotoluminescence spectrum of core-shell QDs 201 have a FWHM in a rangefrom about 20 nm and 40 nm, from about 22 nm and 40 nm from about 24 nmand 40 nm, from about 26 nm and 40 nm, from about 28 nm and 40 nm, fromabout 20 nm and 36 nm, from about 20 nm and 34 nm, or from about 20 nmand 30 nm.

In some embodiments, core-shell QDs 201 may be synthesized to emit lightin one or more various color ranges, such as red, orange, and/or yellowrange. In some embodiments, core-shell QDs 201 may be synthesized toemit light in the green and/or yellow range. In some embodiments,core-shell QDs 201 may be synthesized to emit light in the blue, indigo,violet, and/or ultra-violet range. In some embodiments, core-shell QDs201 may be synthesized to have a primary emission peak wavelengthbetween about 605 nm and about 650 nm, between about 510 nm and about550 nm, or between about 300 nm and about 480 nm.

In some embodiments, core-shell QDs 201 may be synthesized to display ahigh QY. In some embodiments, core-shell QDs 201 may be synthesized todisplay a QY between 80% and 95% or between 85% and 90%.

An Example Method for Forming CdSe/CdS Core-Shell QDs

The following example method demonstrates growth of highly luminescentCdSe/CdS red-emitting QDs having a core/shell structure that may besimilar to QDs 101 and/or 201, as described above. It is understood thatthe following example method is for illustrative purposes only and isnot intended to limit the scope of the present invention. Also, it isunderstood that the following example method can be performed within awide and equivalent range of conditions, formulations and otherparameters without affecting the scope of the invention or anyembodiment thereof.

CdSe cores formation—A solvent was prepared by mixing about 120 g oftrioctylphosphine oxide (TOPO) and about 29 g of tetradecylphosphonicacid (TDPA) in a 500 mL three neck flask. The flask was evacuated to avacuum of about 200 mtorr or below and then refilled with nitrogen. Theevacuation-refill cycle was repeated several times (e.g., three times)to remove air from the system.

About 0.7 M to about 1M Cd precursor stock solution was prepared bymixing tri-octyl phosphine (TOP) with cadmium acetate (Cd(OAc)2). About58 mL of this Cd precursor stock solution in TOP was loaded into a firstsyringe under nitrogen in a glovebox. About 1M to about 2M Se precursorstock solution of trioctylphosphine selenide (TOPSe) was prepared bydissolving Se powder in TOP at room temperature. About 25 mL of this Seprecursor stock solution was loaded into a second syringe under nitrogenin a glovebox. A third and a fourth syringe was loaded with 2.5 mLdiphenylphosphine (DPP) and 60 mL TOP, respectively, under nitrogen in aglovebox.

The Cd precursor solution in the first syringe was quickly injected intothe solvent in the flask to form a first mixture, followed by heating ofthe first mixture to about 250° C. In the first mixture, Cd(OAc)2 isconverted to cadmium tetradecylphosphonate. The first mixture was thencooled down to about 110° C. by air and the reaction by-products such aswater and acetic acid were removed. The DPP in the third syringe wasthen injected into the first mixture to form a second mixture, followedby heating of the second mixture at a temperature between about 280° C.and 350° C. Once the temperature of the second mixture was stabilized,the Se precursor solution in the second syringe was swiftly injectedinto the second mixture to form a third mixture.

Periodically, samples of the third mixture were removed via a syringeand diluted in hexane for visible absorption spectral analysis of thegrowing CdSe cores in the third mixture. Once a desired CdSe core sizewas obtained, the TOP in the fourth syringe was injected into the thirdmixture to form the fourth mixture. Injection of TOP causes a sharp dropof the temperature of the fourth mixture. The fourth mixture is furthercooled by air to about 50° C. The resulting CdSe cores were precipitatedout of the fourth mixture by adding methanol or ethanol to the cooledmixture. The supernatant was removed from the precipitated mixture bycentrifugation and the CdSe cores were obtained and suspended in hexane.

The concentration of the resulting CdSe cores is determined by UV-Visabsorption measurement. In some embodiments, the size of the resultingCdSe cores obtained using the above described method is in a range fromabout 2.0 nm to about 5.0 nm in diameter, from about 3.0 nm to about 5.0nm in diameter, from about 3.5 nm to about 4.5 nm in diameter, fromabout 3.0 nm to about 4.5 nm in diameter, from about 2.5 nm to about 5.0nm in diameter, from about 2.5 nm to about 4.5 nm in diameter, or fromabout 2.5 nm to about 3.5 nm in diameter.

FIG. 3A shows an example TEM image of CdSe cores produced by the examplemethod described above. The size of the resulting CdSe cores is in arange from about 2.5 nm to about 4.5 nm in diameter. The average size ofthe CdSe cores is about 3.5 nm.

It should be noted that besides Cd(OAc)2, other Cd source may be usedfor preparing the Cd precursor stock solution described above withoutdeparting from the spirit and scope of the present invention. In someembodiments, the Cd source is a cadmium iodide, cadmium bromide, cadmiumcarbonate, cadmium acetate, or cadmium hydroxide.

In some embodiments, the Se source for preparing the Se precursor stocksolution described above is selected from trioctylphosphine selenide,tri(n-butyl)phosphine selenide, tri(sec-butyl)phosphine selenide,tri(tert-butyl)phosphine selenide, trimethylphosphine selenide,triphenylphosphine selenide, diphenylphosphine selenide, phenylphosphineselenide, cyclohexylphosphine selenide, octaselenol, dodecaselenol,selenophenol, elemental selenium, hydrogen selenide, bis(trimethylsilyl)selenide, and mixtures thereof. In some embodiments, the selenium sourceis elemental selenium.

CdS shells formation on CdSe cores—Following the core formation process,a solution of the resulting CdSe cores with concentration between about50 mg/mL and about 100 mg/mL was prepared by dispersing the washed CdSecores in ODE. About 3.6 mL of about 66 mg/mL of this CdSe cores in ODEsolution were then injected into a mixture of about 3 mL oleylamine(OYA) and about 6 mL 1-octadecene (ODE) that was prepared in a flask atroom temperature. The CdSe cores in OYA-ODE mixture was then rapidlyheated to about 150° C. Once the temperature reached about 150° C.,about 9.3 mL of about 0.1M Cd precursor stock solution, which may growabout 1 monolayer CdS shells on the CdSe cores, was pumped into theflask at a rate of about 0.5 mL/min. The 0.1M Cd precursor stocksolution was prepared by dissolving cadmium oxide (CdO) in a mixture ofODE, oleic acid (OA), and OYA at a high temperature, followed bydegassing at about 110° C. to remove water.

Following the addition of the Cd precursor, the reaction temperature wasquickly raised to about 310° C. This temperature was maintained untilthe CdS shell growth was completed. After the reaction temperature wasat about 310° C. and held for about 15 min, about 9.3 mL of about 0.1Msulfur precursor stock solution was pumped into the flask at a rate ofabout 0.4 mL/min. The about 0.1M sulfur precursor stock solution wasprepared by mixing 1-octanethiol (OT) in ODE at room temperature (RT).Following about 15 minutes after the addition of the sulfur precursorstock solution, the Cd and S precursor stock solutions were pumped intothe reaction concurrently at a constant rate of about 0.4 mL/min. Theamount of each precursor stock solution was based on the monolayers ofCdS desired. For example, about 110 mL of each stock solution introducedinto the reaction may produce about 6 monolayers of CdS shell on theCdSe cores.

It should be noted that besides CdO, other Cd source may be used forpreparing the Cd precursor stock solution described above withoutdeparting from the spirit and scope of the present invention. In someembodiments, the Cd source is a cadmium iodide, cadmium bromide, cadmiumcarbonate, cadmium acetate, or cadmium hydroxide.

In some embodiments, the sulfur source for preparing the sulfurprecursor stock solution described above is selected from elementalsulfur, octanethiol, dodecanethiol, octadecanethiol, tributylphosphinesulfide, cyclohexyl isothiocyanate, α-toluenethiol, ethylenetrithiocarbonate, allyl mercaptan, bis(trimethylsilyl) sulfide,trioctylphosphine sulfide, and mixtures thereof. In some embodiments,the sulfur source is elemental sulfur.

After the addition of the desired amount of each precursor stocksolutions, the reaction was held at about 310° C. for about another 60min before removing the heat and cooling down the reaction to roomtemperature. The resulting CdSe/CdS core-shell QDs were isolated fromthe reaction mixture in the flask by precipitation with ethanol,followed by centrifugation, decantation of the supernatant, and dryingunder vacuum. The dried CdSe/CdS core-shell QDs were then re-dispersedin cyclohexane for measurements such as QY measurements.

The concentration of the resulting CdSe/CdS core-shell QDs (in nmol/mLor particle/mL) was determined by dividing the nmol or particle numbervalue of the CdSe cores used in the synthesis by the volume of theresulting CdSe/CdS core-shell QDs-cyclohexane solution. The resultingCdSe/CdS core-shell QDs has a narrow size distribution (i.e., a smallFWHM) and a high QY.

In some embodiments, the photoluminescence spectrum of the resultingCdSe/CdS core-shell QD population has a FWHM in a range from about 20 nmand 40 nm, from about 22 nm and 40 nm from about 24 nm and 40 nm, fromabout 26 nm and 40 nm, from about 28 nm and 40 nm, from about 20 nm and36 nm, from about 20 nm and 34 nm, or from about 20 nm and 30 nm.

In some embodiments, the size of the resulting CdSe/CdS core-shell QDsis in a range from about 7.0 nm to about 9.0 nm in diameter, from about7.2 nm to about 9.0 nm in diameter, from about 7.4 nm to about 9.0 nm indiameter, from about 7.6 nm to about 9.0 nm in diameter, from about 7.8nm to about 9.0 nm in diameter, from about 8.0 nm to about 9.0 nm indiameter, from about 7.0 nm to about 8.8 nm in diameter, from about 7.2nm to about 8.6 nm in diameter, from about 7.4 nm to about 8.4 nm indiameter, from about 7.6 nm to about 8.2 nm in diameter, or from about7.8 nm to about 8.0 nm in diameter.

In some embodiments, the resulting CdSe/CdS core-shell QDs emit light inthe red, orange, and/or yellow range. In some embodiments, the resultingCdSe/CdS core-shell QDs have a primary emission peak wavelength betweenabout 605 nm and about 650 nm. In some embodiments, the resultingCdSe/CdS core-shell QDs display a high QY. In some embodiments, theCdSe/CdS core-shell QDs display a QY between 80% and 95% or between 85%and 90%.

FIG. 3B shows an example TEM image of CdSe/CdS core-shell QDs producedby the example methods described above. The size of the CdSe/CdScore-shell QDs is in a range from about 7.5 nm to about 8.5 nm indiameter. The average size of the CdSe/CdS core-shell QDs is about 8 nm.

FIGS. 4A-4B show plots of absorption and photoluminescence spectra ofdifferent concentrations of the reference dye (Rh 640) with anexcitation wavelength of 530 nm, respectively, for QY calculation ofCdSe/CdS core-shell QDs produced by the example methods described above.FIGS. 4C-4D show plots of example absorption and photoluminescencespectra of different concentrations of the CdSe/CdS core-shell QDs withan excitation wavelength of 530 nm. FIG. 4E shows QY measurement of theCdSe/CdS core-shell QDs obtained based on FIGS. 4A-4D. In an embodiment,the QY measurement of the CdSe/CdS core-shell QDs for emission in thered region of the visible spectrum is about 89%.

An Example Method for Forming Barrier Layer Coated Core-Shell QDs

FIGS. 5A-5C illustrates formation of a barrier layer 506 on each ofcore-shell QDs 501 to form barrier layer coated core-shell QDs 500,according to an embodiment. Barrier layer 506 may be similar to barrierlayer 106 and QDs 500 may be similar to QDs 100 described above. In anembodiment, the method of forming barrier layer 506 is based on areverse emulsion method that includes formation of reversemicro-micelles 510. These reverse micro-micelles 510 may serve asreaction centers for coating of core-shell QDs 501 with barrier layer506. In an embodiment, formation of barrier layer 506 may involveformation of reverse micro-micelles 510, incorporation of core-shell QDs501 into reverse micro-micelles 510, and a coating process of theincorporated core-shell QDs 501, as described below. In someembodiments, formation of QDs 500 may additionally or optionally includean acid etch treatment performed after the coating process, that isafter the formation of barrier layer 506. QDs 501 having a core 502 andone or more shells 504 may be similar to core-shell QDs 101, 201, and/orCdSe/CdSe core-shell QDs described above. Core 502 may be similar tocores 101, 202, or CdSe and one or more shells 504 may be similar toshell 104, 204, or CdS described above.

Reverse micro-micelles formation—FIG. 5A illustrates reversemicro-micelles 510 formed in a reverse emulsion (not shown), accordingto an embodiment. Formation of reverse micro-micelles 510 may includeforming a reverse emulsion and adding surfactants 508 in the reverseemulsion. The emulsion may be formed by mixing two immiscible liquidssuch as a hydrophilic polar solvent and a hydrophobic non-polar solvent,according to an embodiment. Water may be used as a polar solvent and ahydrocarbon may be used as a hydrophobic non-polar solvent. Examples ofhydrocarbon that can be used as a hydrophobic non-polar solvent includecyclopentane, cyclohexane, cycloheptane, toluene, or hexane. The twoimmiscible liquids in the reverse emulsion tend to separate into twodistinct phases, a continuous phase and a non-continuous phase, due totheir immiscibility with each other. In some embodiments, the twodistinct phase are a continuous non-aqueous phase (e.g., hydrocarbonphase) and a non-continuous aqueous phase.

In some embodiments, the two distinct phases in the reverse emulsion maybe stabilized by the addition of surfactants 508 to form a firstmixture. Surfactants 508 may be similar to surfactants 108. Someexamples of surfactants 508 include polyoxyethylene (5) nonylphenylether(commercial name IGEPAL CO-520), polyoxyethylene (9) nonylphenylether(IGEPAL CO-630), octylphenoxy poly(ethyleneoxy)ethanol (IGEPAL CA-630),polyethylene glycol oleyl ether (Brij 93), polyethylene glycol hexadecylether (Brij 52), polyethylene glycol octadecyl ether (Brij S10),polyoxyethylene (10) isooctylcyclohexyl ether (Triton X-100),polyoxyethylene branched nonylcyclohexyl ether (Triton N-101),sodiumdioctyl sulfosuccinate, sodium stearate, sodium lauryl sulfate,sodium monododecyl phosphate, sodium dodecylbenzenesulfonate, and sodiummyristyl sulfate.

Surfactants 508 may help to stabilize the non-continuous aqueous phaseby forming a dispersion of reverse micro-micelles 510 in the reverseemulsion to isolate the non-continuous aqueous phase into regimes ofaqueous phases within cores 512 of reverse micro-micelles 510. Each ofthe reverse micro-micelles 510 may be formed by a group of surfactantsfrom among surfactants 508 added into the reverse emulsion. In someembodiments, each of the reverse micro-micelles 510 includes ahydrophilic portion formed by hydrophilic polar groups 508 a (sometimesreferred to as heads in the art) of surfactants 508 and a hydrophobicportion formed by hydrophobic non-polar groups 508 b (sometimes referredto as tails in the art) of surfactants 508. In each of reversemicro-micelles 510, hydrophilic polar heads 508 a soluble in the aqueousphase may form a hydrophilic shell around the aqueous phase containedwithin each of reverse micro-micelle cores 512 and correspondinghydrophobic non-polar tails 508 b soluble in the continuous non-aqueousphase may form a hydrophobic shell surrounding the hydrophilic shell. Insome embodiments, reverse micelles 510 have a spherical shape and thesize of reverse micelles 510 can be controlled by manipulating the typeand/or amount of surfactants 508 added in the reverse emulsion.

Incorporation of core-shell QDs into reverse micro-micelles—Theformation of reverse micro-micelles 510 may be followed by incorporationof core-shell QDs 501 into cores 512 of reverse micro-micelles 510, asillustrated in FIG. 5B. In an embodiment, this incorporation processincludes forming a QD solution having core-shell QDs 501 dispersed in asolvent (e.g., cyclohexane, toluene, or hexane). The QD solution may beformed in a process similar to that described above with reference toQDs 201 and CdSe/CdSe core-shell QDs. The incorporation process furtherincludes forming a second mixture of the QD solution and the firstmixture having reverse micro-micelles 510, according to an embodiment.

Similar to QDs 201, and/or CdSe/CdSe core-shell QDs described above, QDs501 may have native ligands or surfactants (not shown) bonded on theouter surface of the outermost shell 504 before adding to the reverseemulsion. These native ligands or surfactants of QDs 501 may havesimilar affiliation to QDs 501 as the hydrophilic polar heads 508 a ofsurfactants 508. The native ligands or surfactants (not shown here) maybe dynamically bonded to QDs 501, i.e. the native ligands or surfactantsmay be bonded to QDs 501 in an on-and-off fashion, which may provide theopportunity for the native ligands or surfactants to be substituted bysurfactants 508 in the reverse emulsion. In some embodiments, thesenative ligands or surfactants of QDs 501 have hydrophilic groups, whichcauses QDs 501 in the second mixture to be drawn to the aqueous phasesisolated within cores 512 of reverse micro-micelles 510 and be enclosedwithin cores 512, as illustrated in FIG. 5B. Each of these QD-filledreverse micro-micelles 510 in the second mixture provides an environmentor a reaction center for the formation of barrier layer 506 on each ofthe QDs 501 enclosed within the reverse micro-micelles 510.

In some embodiments, each of the reverse micro-micelles 510 encloses oneof the QDs 501 in the second mixture. Such one-in-one incorporation ofQDs 501 into reverse micro-micelles 510 may help to prevent aggregationof the QDs 501 with each other and allow individual coating of the QDs501 with a barrier layer 506. In some embodiments, during the formationof barrier layer 506, substantially all the native ligands orsurfactants of QDs 501 may be exchanged or replaced by the surfactantsof the reverse micro-micelles. In some embodiments, after one or more ofthe QDs 501 are individually enclosed by a barrier layer 506, there maybe no native ligands or surfactants left between QDs 501 and the barrierlayer 506. Instead, the native ligands or surfactants may be driven outof the interface between QDs 501 and barrier layer 506 into thecontinuous hydrophobic phase. The native ligands or surfactants in thecontinuous hydrophobic phase may be bonded to the surface of the barrierlayer 506. It should be noted that even though FIG. 5A-5B illustrates anequal number of QDs 501 and reverse micro-micelles 510, a person skilledin the art would understand based on the description herein that in someembodiments the number of reverse micro-micelles, similar to reversemicro-micelles 510, formed in the reverse emulsion may be greater thanthe number of core-shell QDs, similar to core-shell QDs 501, added tothe reverse emulsion. In such embodiments, some of the reverse micellesmay remain empty of core-shell QDs.

Barrier Layer formation—According to an embodiment, following theincorporation of QDs 501 into the reverse micro-micelles 510 in thesecond mixture, barrier layer 506 is formed on each of the incorporatedQDs 501, as illustrated in FIG. 5C. In an embodiment, the formation ofbarrier layer 506 includes forming a third mixture of one or moreprecursors that have elements of barrier layer 506 and the secondmixture. For example, Al, Ba, Ca, Mg, Ni, Si, Ti, or Zr precursor may beadded to the second mixture for forming barrier layer 506 comprisingoxides and/or nitrides of Al, Ba, Ca, Mg, Ni, Si, Ti, or Zr. In someembodiments, tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate,tetrapropyl orthosilicate, or tetrabutyl orthosilicate is used as a Siprecursor. The one or more precursors may be prepared as a solution andadded into the second mixture at a rate between about 6 mL/min and 8m/min, while the second mixture may be rigorously stirred.

The formation of barrier layer 506 further includes forming a fourthmixture of one or more catalysts and the third mixture, according to anembodiment. In an embodiment, ammonia is added as a catalyst to thethird mixture. The one or more catalysts may be prepared as a solutionand added into the third mixture at a rate between about 4 mL/min and 7mL/min, while the third mixture may be rigorously stirred. Both theadded precursors and catalysts are drawn to QDs 501 in the aqueous phaseof reverse micelles 510 due to their affiliation with the hydroxyl (OH)group. Once the added precursor and catalysts are enclosed with acorresponding one of the QDs 501 within each of the reverse micelles510, the added one or more precursors undergo catalyzed hydrolysis totransform into an intermediate form (hydrolyzed silicon precursor). Insome embodiments, surfactants 508 bonded to QDs 501 are completelysubstituted by hydrolyzed silicon precursors to form a monolayer ofhydrolyzed silicon precursors, which further undergo condensation toform an individual coating of barrier layer 506 around the correspondingone of the QDs 501. For example, once a Si precursor such as TEOS andammonia catalyst are drawn into and enclosed with a corresponding one ofthe QDs 501 within reaction center provided by each of the reversemicro-micelles 510, TEOS undergoes ammonia catalyzed hydrolysis totransform into an intermediate form, tetrahydroxysilane, which furtherundergoes condensation to form an individual coating of SiO2 barrierlayer 506 around the corresponding one of the QDs 501. In someembodiments, this hydrolysis and condensation of the one or moreprecursors added is performed without stirring and/or heating the fourthmixture. In some embodiments, this hydrolysis and condensation reactionmay be allowed to occur from about 1 day to about 7 days untilsubstantially all of the one or more precursors in the fourth mixtureare used up.

The thickness of the barrier layer 506 formed may be controlled bymanipulating, independently or in combination, parameters such as theamount of precursor, the concentration of QDs, and the hydrolysis andcondensation reaction time. In an embodiment, increasing theconcentration or number of QDs 501 in the second mixture for the sameamount of precursors in the third mixture may reduce the thickness ofthe barrier layer 506.

In alternate embodiments, the amount of the one or more precursors thatmay be needed to achieve the desired thickness of barrier layer 506 isadded in two or more stages of the barrier layer growth process. Forexample, a portion of the precursor amount may be added to the secondmixture to make the third mixture and the remaining portion of theprecursor amount may be added to the fourth mixture after the precursorsof the third mixture has been used up during the hydrolysis andcondensation reaction.

Barrier layer 506 may be grown to a thickness 506 t ranging from about 8nm to about 15 nm in various embodiments. In some embodiments, thickness506 t may have a minimum value such that a center-to-center distancebetween two adjacent QDs 500, for example, in a solution, composition,and/or film is equal to or greater than a Forster radius. In someembodiments, thickness 506 t may have a minimum value of between about 8nm to about 15 nm.

Acid Etch Treatment—After the growth of barrier layer 506 to a desiredthickness, an acid etch treatment may be performed on QDs 500, accordingto an embodiment. In some embodiments, one or more acids may be added tothe fourth mixture to form a fifth mixture. Examples of the one or moreacids include acetic acid, hydrochloric acid, nitric acid, a fatty acid,or a combination thereof. In some embodiments, the molar ratio in arange from about 1.5 to about 10 may be maintained between the one ormore acids and the one or more catalysts in the fifth mixture. In oneembodiment, the molar ratio of about 2 may be maintained between aceticacid and ammonium hydroxide catalyst in the fifth mixture. The etchingprocess in the fifth mixture may be performed for a time period rangingfrom about 5 minutes to about 2 days. The acid etch rate may be variedby varying the concentration of the one or more acids added to thefourth mixture, etching temperature, molar ratio between the one or moreacids to the one or more catalysts, and/or thickness of barrier layer506.

This post-coating acid etch treatment of QDs 500 may help tosubstantially reduce quenching in the optical emission properties of QDs501. Such optical quenching may be due to reaction of QDs 501 withchemicals used during processing (e.g., catalyst used during barrierlayer coating process) on QDs 501 prior to the etching process. Forexample, the use of ammonium hydroxide catalyst may create coordinatingsites on surfaces 501 s of QDs 501 for OH⁻ and NH₄ ⁺ ions. These ionsmay serve as photoelectron trap sites on surfaces 501 s, and thephotoelectron trap sites may induce quenching in the optical emissionproperties of QDs 501. The etching of surfaces 501 s during the acidetch treatment may help to etch off such photoelectron trap sites and/orother trap sites and/or defects on surfaces 501 s of QDs 501 that induceoptical quenching of QDs 501, and consequently, substantially reducequenching in the optical emission properties of QDs 501. The acid etchtreatment of barrier layer coated QDs 500 may be continued until QY ofQDs 500 is substantially similar to QY of uncoated QDs 501. That is theacid etch treatment may be continued until negative effects ofprocessing on QDs 501 (e.g., negative effects of buffered barrier layercoating process) are substantially reduced.

It should be noted that even though barrier layers 506 may be present onQDs 501, acid molecules or H⁺ ions from the one or more acids in thefifth mixture can penetrate through barrier layer 506, which are porous,and arrive at surfaces 501 s.

In some embodiments, the acid etch treatment may be performed on QDs 501prior to and post the barrier layer 506 formation process.

In some embodiments, the one or more catalysts (e.g., ammoniumhydroxide) may be selectively removed, for example by evaporating beforeadding the one or more acids (e.g., acetic acid) to the fourth mixtureto form the fifth mixture for the acid etch treatment of QDs 500.

The acid etch treatment may be followed by removal of the solvent, theunreacted one or more precursors, the one or more catalysts, andreaction byproducts are removed from the fifth mixture. In someembodiments, the solvent, unreacted precursors, and reaction byproductsmay be removed by evaporation at a temperature between about 40° C. andabout 60° C. under vacuum. The resulting concentrate after removal ofthe solvent and precursors may be further dried at a temperature betweenabout 50° C. and about 70° C. under vacuum for about 60 min to about 90min. In some embodiments, the resulting barrier layer coated core-shellQDs 500 may be isolated after the acid etch treatment by precipitationwith a solvent (e.g., ethanol) and centrifugation and re-dispersed in ahydrophobic solvent such as but not limited to toluene.

The removal of the solvent, the unreacted one or more precursors, theone or more catalysts, and reaction byproducts by vacuum evaporation mayensure that surfactants 508 remain bonded to the outer surface of QDs500 as illustrated in FIG. 5C. The hydrophobic tails 508 b ofsurfactants 508 on barrier layer 506 provide a hydrophobic shell thatensures the dispersability of the resulting dried and isolated QDs 500in hydrophobic environments (e.g., toluene, photoresist materials) forcompatibility with, for example, device fabrication processes withoutadversely affecting the optical properties of the QDs 500.

In contrast to the above described post-synthesis process of QDs 500,current post-synthesis process of QDs typically includes washing thesynthesized QDs in hydrophilic solvents such as ethanol, methanol, orwater to separate the synthesized QDs from the reaction solution. Thewashing is then followed by re-dispersing of the washed QDs inhydrophilic alcohols such as ethanol or methanol. The re-dispersed QDsare then subjected to a ligand exchange process at high temperatures(e.g., about 200° C.) to introduce a new surfactant on the re-dispersedQDs. The introduction of the new surfactant is to provide a hydrophobicshell on the QDs, as the surfactants that may be present on thesynthesized QDs are removed during the washing. The exposure to water orhydrophilic solvents in current post-synthesis process of QDs quenchesthe optical emission properties of the washed QDs as water hasnon-radiative centers that adversely affects the emission properties ofthe washed QDs. The high temperature ligand exchange process also has anegative effect on the optical emission properties of the QDs.

The isolated and re-dispersed QDs 500 may have a narrow sizedistribution (i.e., a small FWHM) and a high QY similar to QDs 501. Insome embodiments, the photoluminescence spectrum of both QDs 501 and 500have a FWHM in a range from about 20 nm and 40 nm, from about 22 nm and40 nm from about 24 nm and 40 nm, from about 26 nm and 40 nm, from about28 nm and 40 nm, from about 20 nm and 36 nm, from about 20 nm and 34 nm,or from about 20 nm and 30 nm.

In some embodiments, both QDs 500 and 501 may emit light in one or morevarious color ranges, such as red, orange, and/or yellow range. In someembodiments, both QDs 500 and 501 emit light in the green and/or yellowrange. In some embodiments, both QDs 500 and 501 may emit light in theblue, indigo, violet, and/or ultra-violet range. In some embodiments,both QDs 500 and 501 may have a primary emission peak wavelength between605 nm and 650 nm, between 510 nm and 550 nm, or between 300 nm and 480nm.

In some embodiments, both QDs 500 and 501 display a high QY. In someembodiments, both QDs 500 and 501 display a QY between 80% and 95% orbetween 85% and 90%.

Thus, according to various embodiments, the presence of barrier layer506 on QDs 501 does not substantially change or quench the opticalemission properties of QDs 501.

In some embodiments, barrier layer coated QDs 500 subjected to acid etchtreatment display a QY that is about 10% to about 20% higher than QYdisplayed by barrier layer coated QDs without acid etch treatment.

It should be noted that three reverse micro-micelles 510, three coreshell QDs 501, and three barrier layer coated core-shell QDs 500 havebeen shown in FIGS. 5A-5C, respectively, for illustrative purposes.However, as would be understood by a person of skill in the art based onthe description herein, the methods described above can produce anynumber of reverse micro-micelles, core shell QDs, and barrier layercoated core-shell QDs similar to reverse micro-micelles 510, core shellQDs 501, and barrier layer coated core-shell QDs 500, respectively.

An Example Method for Forming SiO2 Coated CdSe/CdS Core-Shell QDs

The following example method demonstrates growth of highly luminescentSiO2 coated CdSe/CdS red-emitting QDs (also referred herein as SiO2coated QDs). The SiO2 coated QDs may be similar to QDs 100 and/or 500,according to an embodiment. The SiO2 coated QDs have a core/shellstructure that may be similar to QDs 101, 201, and/or 501 and also havea SiO2 barrier layer that may be similar to barrier layer 106 and/or 506described above. It is understood that the following example method isfor illustrative purposes only and is not intended to limit the scope ofthe present invention. Also, it is understood that the following examplemethod can be performed within a wide and equivalent range ofconditions, formulations and other parameters without affecting thescope of the invention or any embodiment thereof.

Formation of CdSe/CdS Core-Shell QDs—These QDs were prepared using theexample method for forming CdSe/CdS core-shell QDs described above. A QDsolution of about 230 nmol of the synthesized and dried CdSe/CdScore-shell QDs in cyclohexane was prepared.

Reverse micro-micelles formation—A first mixture of stabilized reverseemulsion having reverse micro-micelles was prepared by mixing about 100mL IGEPAL CO-520, a surfactant, with about 750 mL cyclohexane in a ILbottle. The first mixture was stirred for about 20 min.

Incorporation of CdSe/CdS QDs into reverse micro-micelles—After theabout 20 min stirring of the first mixture, a second mixture wasprepared by adding the QD solution to the first mixture. The secondmixture was stirred for about 20 min after the addition of the QDsolution.

Barrier Layer formation—Following the about 20 min stirring of thesecond mixture, a third mixture was prepared by adding about 7.4 mL ofTEOS, a Si precursor, to the second mixture at a rate of about 7.4mL/min, while the second mixture was rigorously stirred. The thirdmixture was stirred for about 20 min after the addition of TEOS and wasfollowed by preparation of a fourth mixture. The fourth mixture wasprepared by adding about 13.8 mL 30% ammonium hydroxide solution, acatalyst, to the third mixture at a rate of about 4.6 mL/min to about6.9 mL/min, while the third mixture was rigorously stirred. The fourthmixture was stirred for about 2 min after the addition of the catalyst.Following the about 2 min stirring, the bottle including the fourthmixture was capped and stored for about 1 to about 7 days withoutstirring or heating the fourth mixture.

At the end of the 1 to 7-day reaction, the solvent, the unreacted TEOS,the ammonium hydroxide, and reaction byproducts such as ethanol wereevaporated at or below a temperature of about 50° C. under vacuum toyield SiO2 coated QDs having surfactant IGEPAL CO-520 on their outersurfaces similar to, for example, QDs 500 described above. The resultingSiO2 coated QDs were further dried at or below a temperature of about60° C. under vacuum for about 60 min to remove substantially allmoisture from them. Following the drying of the SiO2 coated QDs, theywere isolated by precipitation and centrifugation and re-dispersed intoluene to form a stable hydrophobic solution.

The re-dispersed SiO2 coated QDs exhibited a narrow size distribution(i.e., a small FWHM) and a high QY. In some embodiments, thephotoluminescence spectrum of the SiO2 coated QD population has a FWHMin a range from about 20 nm and 40 nm, from about 22 nm and 40 nm fromabout 24 nm and 40 nm, from about 26 nm and 40 nm, from about 28 nm and40 nm, from about 20 nm and 36 nm, from about 20 nm and 34 nm, or fromabout 20 nm and 30 nm.

In some embodiments, the size of the resulting SiO2 coated CdSe/CdS QDsis in a range from about 20 nm to about 50 nm in diameter, from about 24nm to about 50 nm in diameter, from about 28 nm to about 50 nm indiameter, from about 32 nm to about 50 nm in diameter, from about 35 nmto about 50 nm in diameter, from about 20 nm to about 45 nm in diameter,from about 24 nm to about 45 nm in diameter, from about 30 nm to about45 nm in diameter, from about 35 nm to about 45 nm in diameter, or fromabout 25 nm to about 35 nm in diameter. In some embodiments, the averagesize of the SiO2 coated CdSe/CdS core-shell QDs is about 25 nm, about 35nm, or about 40 nm.

In some embodiments, the thickness of the SiO2 barrier layer of the SiO2coated QDs is in a range from about 8 nm to about 20 nm, from about 10nm to about 20 nm, from about 15 nm to about 20 nm, from about 8 nm toabout 15 nm, or from about 10 nm to about 15 nm.

In some embodiments, the SiO2 coated QDs emit light in the red, orange,and/or yellow range. In some embodiments, the resulting SiO2 coated QDshave a primary emission peak wavelength between about 605 nm and about650 nm, between about 615 nm and about 640 nm, between about 620 nm andabout 635 nm, or between about 625 nm and about 630 nm.

In some embodiments, the SiO2 coated QDs display a QY between 80% and95% or between 85% and 90%.

FIG. 6 shows an example TEM image of a plurality of SiO2 coated CdSe/CdSQDs 600 produced by the example methods described above. Each SiO2coated CdSe/CdS QDs 600 includes a CdSe/CdS QD 601 and a SiO2 barrierlayer 606 surrounding the CdSe/CdS QD 601. The size of the SiO2 coatedCdSe/CdS QDs is in a range from about 31 nm to about 35 nm in diameter.

FIGS. 7A-7B show example optical performance plots of SiO2 coatedCdSe/CdS QDs and CdSe/CdS QDs, respectively, over a period of time whenexposed to continuous 200 mW/cm² flux at 450 nm. These SiO2 coatedCdSe/CdS QDs and CdSe/CdS QDs are produced by the example methodsdescribed above. Comparison of the optical performances in FIGS. 7A and7B shows the SiO2 coated CdSe/CdS QDs exhibiting a higher stabilityperformance over a period of time under high flux light exposurecompared to the CdSe/CdS QDs without the SiO2 coating. This comparisondemonstrates that the SiO2 barrier layer helps to protect the coatedCdSe/CdS QDs from harsh environment.

Example optical properties of SiO2 coated CdSe/CdS QDs and CdSe/CdS QDsproduced by the example methods described above are presented in Table 1below. As shown in Table 1, for both sizes of SiO2 coated CdSe/CdS QDs,the SiO2 barrier layer formation process and/or presence of the SiO2barrier layer coating on the CdSe/CdS QDs does not quench or degrade theoptical properties of the CdSe/CdS QDs. There is hardly any differenceobserved between the optical properties of the CdSe/CdS QDs with andwithout the SiO2 coating, as shown in Table 1. The higher QY observed inthe 25 nm SiO2 coated QDs than the 35 nm SiO2 coated QDs may be due to ahigher amount of fluorescence quenching precursors and catalysts such asTEOS, ammonium hydroxide, and water being assigned to the QDs in thereverse micro-micelles during the formation of the 35 nm QDs havingthicker SiO2 coating that the 25 nm SiO2 coated QDs.

TABLE 1 Example optical data for CdSe/CdS QDs and SiO2 coated CdSe/CdSQDs Average size of QDs in Sample diameter Emission FWHM QY No. (nm)Description Wavelength (nm) (nm) (%) 1 CdSe/CdS QDs 627.8 23.9 89.4 2 25SiO2 coated CdSe/CdS QDs 626.7 24.9 92.6 3 SiO2 coated CdSe/CdS QDs627.1 24.9 93.9 4 SiO2 coated CdSe/CdS QDs 627.7 25.1 92.4 5 SiO2 coatedCdSe/CdS QDs 627.1 25.0 93.3 6 SiO2 coated CdSe/CdS QDs 627.5 25.3 92.47 CdSe/CdS QDs 630.1 27.3 86.9 8 35 SiO2 coated CdSe/CdS QDs 629.6 27.582.4 9 SiO2 coated CdSe/CdS QDs 629.1 27.6 84.3 10 SiO2 coated CdSe/CdSQDs 629.5 27.2 82.3 11 SiO2 coated CdSe/CdS QDs 630.9 28.0 80.7 12 SiO2coated CdSe/CdS QDs 630.8 28.2 84.8

Example Steps for Forming Barrier Layer Coated Core-Shell QDs

FIG. 8 illustrates a flowchart for making barrier layer coatedcore-shell QDs, according to an embodiment. Method 800 may be performedto form QDs similar to QDs 100, 101, 201, 500, 501, 600, and 601. Method800 is not intended to be exhaustive and other steps may be performedwithout deviating from the scope or spirit of the invention. Solely forillustrative purposes, the steps illustrated in FIG. 8 will be describedwith reference to example processes illustrated in FIGS. 2A-2B and5A-5C. Steps can be performed in a different order or not performeddepending on specific applications.

In step 802, a QD solution having core-shell QDs is formed, according toan embodiment. For example, QD solution having core-shell QDs may beproduced by dispersing core-shell QDs such as QDs 101, 201, and/or 501in a solvent (e.g., cyclohexane, toluene, or hexane).

In step 804, reverse micro-micelles formed in a stabilized reverseemulsion, according to an embodiment. For example, reversemicro-micelles in a stabilized reverse emulsion may be produced byforming a first mixture of one or more surfactants (e.g., IGEPAL CO-520,IGEPAL CO-630, IGEPAL CA-630, Triton X-100, or Brij 53) with hydrophobicsolvents such as, but not limited to, cyclopentane, cyclohexane, orcycloheptane and stirring the first mixture for about 20 min.

In step 806, the core-shell QDs are incorporated into the reversemicro-micelles, according to an embodiment. For example, the core-shellQDs are incorporated into the reverse micro-micelles by forming a secondmixture of the QD solution and the first mixture and stirring the secondmixture for about 20 min.

In step 808, the incorporated QDs are individually coated with a barrierlayer, according to an embodiment. For example, the incorporated QDs areindividually coated with a barrier layer by forming a third mixture ofone or more precursor solution and the second mixture and stirring thethird mixture for about 20 min. The formation of third mixture isfollowed by forming a fourth mixture of one or more catalysts and thethird mixture and stirring the fourth mixture for about 2 min. Followingthe about 2 min stirring, the bottle including the fourth mixture iscapped and stored for 7 days without stirring or heating the fourthmixture.

In step 810, the resulting barrier layer coated QDs are subjected to anacid etch treatment, according to an embodiment. For example, theresulting barrier layer coated QDs are subjected to an acid etchtreatment by forming a fifth mixture of one or more acids and the fourthmixture and treating the resulting barrier layer coated QDs in the fifthmixture for about 12 hours. In some embodiments, step 810 may be anoptional step.

In step 812, the barrier layer coated QDs are isolated from the fifthmixture, according to an embodiment. For example, the acid etch treatedbarrier layer coated QDs are isolated by evaporating the solvent, theunreacted precursors, the catalysts, and reaction byproducts at or belowa temperature of about 50° C. under vacuum to yield barrier layer coatedQDs having surfactants on their outer surfaces similar to, for example,QDs 500 described above. The evaporation is followed by further dryingof the acid etch treated barrier layer coated QDs at a temperature ofabout 60° C. under vacuum for about 60 min to remove substantially allmoisture from them. Following the drying, the acid etch treated barrierlayer coated QDs are isolated by precipitation and centrifugation.

An Example Embodiment of a QD Film

Light emitting QDs such as QDs 100, 500, and/or 600 discussed above maybe used in a variety of applications that benefit from having sharp,stable, controllable, and defined angular optical emissions in thevisible and infrared spectrum. Such applications may use the lightemitting QDs in the form of a QD film 900 as shown in FIG. 9. In someapplications, the light emitting QDs may be cast as a QD film 900 on asubstrate and patterned by a photolithographic process. Display devicessuch as organic light emitting diode (OLED) display devices or liquidcrystal display (LCD) devices may use such a QD film 900, for example asa color down conversion layer. In such display devices, QD film 900 maybe part of their display panel or pixel units of their display panel andmay be disposed on light sources or substrates of the display devices,according to some embodiments.

Typically, non-QD-based color down conversion layers in display devicescan range from about 1 μm to about 10 μm in thickness. In order toachieve similar or higher optical density and QY from QD-based colordown conversion layers of similar thickness, such as QD film 900, alarge density of QDs may need to be loaded and closely packed (i.e.,adjacent QDs in substantial contact with each other) within QD film 900without the QDs being aggregated with each other. However, QDs preparedby current methods tend to aggregate and/or reabsorb emission ofadjacent QDs when closely packed in a QD film and consequently, due toquenching of their optical properties, suffer from lower QY compared tonon-QD-based color down conversion layers. In some embodiments, suchproblems may be overcome by using QD films of barrier layer coatedcore-shell QDs such as QDs 100, 500, and/or 600. The barrier layer mayhelp to prevent these QDs from aggregating and reabsorbing each other'semission and consequently, achieve high optical density and QY even whenthese QDs are closely packed in a QD film of about 1 μm to about 3 μm.The barrier layer of these QDs may also help to protect them from harshenvironments (e.g., heat, chemicals) during processing of QD films.

The barrier layer coated core-shell QDs such as QDs 100, 500, and/or 600in QD films such as QD film 900 may also help to achieve thinner and/orsingle layered QD-based color conversion optical films compared tocurrent multi-layered QD-based color conversion optical films ofQD-based display devices. The thinner and/or single layered QD-basedcolor conversion optical films may meet the requirements for colorconversion optical films in today's mobile display applications and/orfuture display applications such as wearable display devices. Some ofthese requirements may be for color conversion optical films having amaximum thickness of less than about 75 μm, a defined angular lightemission property, and/or a minimal or no edge degradation aroundperimeters of the color conversion optical films.

The current multi-layered QD-based color conversion optical films arenot able to meet such requirements, which may be critical for mobiledisplay applications that require thin as possible components andbezel-free displays. These current multi-layered QD-based optical filmsinclude QD films interposed between polymer plastic based substratesthat serve as barrier films to protect the QDs in the QD films fromambient environment and/or supporting structures for the QD films. Suchuse of polymer plastic based substrates make the total thickness ofthese current optical films equal to or greater than about 175 μm. Asthe barrier layer coated core-shell QDs such as QDs 100, 500, and/or 600in QD films such as QD film 900 are individually coated with barrierlayers, the use of polymer plastic based substrates can be eliminated.As a result, the thickness of color conversion optical films having QDfilms such as QD film 900 may be reduced to less than about 75 μm. Insome embodiments, QD film 900 may include barrier layer coatedcore-shell QDs such as QDs 100, 500, and/or 600 embedded in polymerplastic film that are optically transparent to the optical emissionsfrom the embedded QDs. The polymer plastic film may provide mechanicalsupport and additional protection from environment to QD film 900without increasing its total thickness over the maximum thicknessrequirement in display applications.

Also, in order to achieve defined angular optical emission additionaloptical films such as brightness enhancement films (BEFs) may be used inthese current optical films, which increases their total thickness over175 μm. In some embodiment, defined angular optical emission may beachieved in color conversion optical films having QD films such as QDfilm 900 without using such BEFs. In some embodiments, barrier layercoated core-shell QDs such as QDs 100, 500, and/or 600 may be embeddedin BEFs or other optically transparent layers of display devices to formQD films such as QD film 900.

It is to be appreciated that QD films such as QD film 900 includingbarrier layer coated core-shell QDs such as QDs 100, 500, and/or 600embedded in polymer plastic films, BEFs, or other optically transparentlayers, as discussed above, may not require any additional substratesfor casting the barrier coated QDs and/or for supporting the QD films.In some embodiments, QD films such as QD film 900 may be stacked withother optical film and such stack may have a thickness in a range fromabout 70 μm to about 200 μm.

FIG. 9 illustrates a cross-sectional view of a QD film 900, according toan embodiment. QD film 900 may include a plurality of barrier layercoated core-shell QDs 902 and a matrix material 910, according to anembodiment. QDs 902 may be similar to QDs 100, 500, and/or 600 instructure, function, and/or characteristics and may be embedded orotherwise disposed in matrix material 910, according to someembodiments. As used herein, the term “embedded” is used to indicatethat the QDs are enclosed or encased within matrix material 910 thatmakes up the majority component of the matrix. It should be noted thatQDs 902 may be uniformly distributed throughout matrix material 910 inan embodiment, though in other embodiments QDs 902 may be distributedaccording to an application-specific uniformity distribution function.It should be noted that even though QDs 902 are shown to have the samesize in diameter, a person skilled in the art would understand that QDs902 may have a size distribution. Similar to QDs 500, and/or 600, QDs902 may have a narrow size distribution and high QY.

In an embodiment, QDs 902 may include a homogenous population of QDshaving sizes that emit in the blue visible wavelength spectrum, in thegreen visible wavelength spectrum, or in the red visible wavelengthspectrum. In other embodiments, QDs 902 may include a first populationof QDs having sizes that emit in the blue visible wavelength spectrum, asecond population of QDs having sizes that emit in the green visiblewavelength spectrum, and a third population of QDs that emit in the redvisible wavelength spectrum.

Matrix material 910 may be any suitable host matrix material capable ofhousing QDs 902. For example, BEFs or other optically transparent layerof display devices may be the host matrix material to house QDs 902.Suitable matrix materials may be chemically and optically compatiblewith QDs 902 and any surrounding packaging materials or layers used inapplying QD film 900 to devices. Suitable matrix materials may includenon-yellowing optical materials which are transparent to both theprimary and secondary light, thereby allowing for both primary andsecondary light to transmit through the matrix material. In anembodiment, matrix material 910 may completely surround each of the QDs902. The matrix material 910 may be flexible in applications where aflexible or moldable QD film 900 is desired. Alternatively, matrixmaterial 910 may include a high mechanical strength, non-flexiblematerial.

In another embodiment, matrix material 910 may have low oxygen andmoisture permeability, exhibit high photo- and chemical-stability,exhibit favorable refractive indices, and adhere to outer surfaces ofQDs 902, thus providing an air-tight seal to protect QDs 902. In anotherembodiment, matrix material 910 may be curable with UV or thermal curingmethods to facilitate roll-to-roll processing.

Matrix material 910 may include polymers and organic and inorganicoxides. In some embodiments, matrix material 910 may be an extrudablematerial, that is a material that may be capable of being extruded in afilm extrusion process. Suitable polymers for use in matrix material 910may be any polymer known to the ordinarily skilled artisan that can beused for such a purpose. The polymer may be substantially translucent orsubstantially transparent. Matrix material 910 may include, but notlimited to, epoxies, acrylates, norbornene, polyethylene, poly(vinylbutyral):poly(vinyl acetate), polyurea, polyurethanes, polypropylene,polycarbonate, or a combination thereof; silicones and siliconederivatives including, but not limited to, amino silicone (AMS),polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane,polydialkylsiloxane, silsesquioxanes, fluorinated silicones, and vinyland hydride substituted silicones; acrylic polymers and copolymersformed from monomers including, but not limited to, methylmethacrylate,butylmethacrylate, and laurylmethacrylate; styrene-based polymers suchas polystyrene, amino polystyrene (APS), and poly(acrylonitrile ethylenestyrene) (AES); polymers that are crosslinked with bifunctionalmonomers, such as divinylbenzene; cross-linkers suitable forcross-linking ligand materials, epoxides which combine with ligandamines (e.g., APS or PEI ligand amines) to form epoxy, and the like.

In some embodiments, matrix material 910 includes scattering microbeadssuch as TiO2 microbeads, ZnS microbeads, or glass microbeads that mayimprove photo conversion efficiency of QD film 900.

According to some embodiments, QD film 900 may be formed by mixing QDs902 in a polymer (e.g., photoresist) and casting the QD-polymer mixtureon a substrate, mixing QDs 902 with monomers and polymerizing themtogether, mixing QDs 902 in a sol-gel to form an oxide, or any othermethod known to those skilled in the art.

According to some embodiments, the formation of QD film 900 may includea film extrusion process as illustrated in FIG. 9A. The film extrusionprocess may include forming a homogenous mixture 911 of matrix material910 and barrier layer coated core-shell QDs such as QDs 100, 500, and/or600, introducing the homogenous mixture into a top mounted hopper 914that feeds into an extruder 916. In some embodiments, the homogenousmixture 911 may be in the form of pellets. The film extrusion processmay further include extruding QD film 900 from a slot die 918 andpassing extruded QD film 900 through chill rolls 920. In someembodiments, the extruded QD film 900 may have a thickness less thanabout 75 μm, for example, in a range from about 70 μm to about 40 μm,from about 65 μm to about μm, from about 60 m to about 40 μm, or fromabout 50 μm to about 40 μm. In some embodiments, the formation of QDfilm 900 may optionally include a secondary process followed by the filmextrusion process. The secondary process may include a process such asco-extrusion, thermoforming, vacuum forming, plasma treatment, molding,and/or embossing to provide a texture 913 to a top surface 900 s of QDfilm 900, as shown in a cross-sectional view of QD film 900 in FIG. 9B.The textured top surface 900 s of QD film 900 may help to improve, forexample defined optical diffusion property and/or defined angularoptical emission property of QD film 900.

FIG. 10 shows an example photoluminescence spectrum of a QD filmincluding SiO2 coated CdSe/CdS QDs in a matrix material. The SiO2 coatedCdSe/CdS QDs are produced by the example methods described above. Plot1020 of FIG. 10 illustrates the primary emission peak wavelength of theQD film at about 625 nm for an excitation peak wavelength at about 405nm.

Table 2 below shows example optical data for two sets of QD films asfunction of baking temperature. The two sets of QD films were preparedby mixing SiO2 coated CdSe/CdS QDs with a carboxyl acrylate polymer,dispersing the mixture in an organic solvent, and casting theQDs-polymer-solvent blend into a layer of about 2 μm to about 4 μm thickby spin-coating on substrates. The QD films were then baked at differenttemperatures and their optical properties were measured. One set of QDfilms was prepared with SiO2 coated CdSe/CdS QDs having an average sizeof about 25 nm in diameter and the other set of QD films was preparedwith SiO2 coated CdSe/CdS QDs having an average size of about 35 nm indiameter. Both sizes of SiO2 coated CdSe/CdS QDs were prepared by theexample methods described above.

As illustrated by the optical data in Table 2, the two sets of QD filmsexhibit external quantum efficiency (EQE) at about 50% for a bakingtemperature of about 250° C. This EQE is much higher than the EQEobserved for QD films having CdSe/CdS QDs without the SiO2 barrierlayer. The optical data in Table 2 also shows that very smalldifferences are observed between the FWHMs and the emission wavelengthsof the SiO2 coated CdSe/CdS QDs and the QD films. Such small differencesmay indicate that the SiO2 barrier layer prevented aggregation of theSiO2 coated CdSe/CdS QDs and quenching of their optical properties evenwhen they are closely packed in the QD films to achieve high opticaldensity as in Table 2.

TABLE 2 Example optical data for QD films as a function of baitingtemperature Average size of QY of FWHM Emission Wave- Baking EmissionWave- FWHM of Sample QDs in diameter QDs of QDs length of QDs temp. EQEOptical length of QD film QD film No. (nm) (%) (nm) (nm) (° C.) (%)density (nm) (nm) 1 25 84.8 28.2 630.8 60 64.66 0.265 630.42 26.96 2 18061.61 0.247 627.07 25.73 3 250 49.60 0.244 625 25 4 35 80.7 28 630.9 6063.46 0.325 631.54 27.72 5 180 56.7 0.326 625 25 6 250 51.4 0.270 625 25

Table 3 below shows example optical data for a QD film as function ofexposure to air over a period of time. The QD film was prepared bymixing SiO2 coated CdSe/CdS QDs with a carboxyl acrylate polymer,dispersing the mixture in an organic solvent, and casting theQDs-polymer-solvent blend into a layer of about 1 μm to about 10 μmthick by spin-coating on a substrate, followed by baking the QD film atabout 250° C. for about 30 minutes. The QD film was exposed to air fordifferent periods of time and its optical properties were measured. TheSiO2 coated CdSe/CdS QDs were prepared by the example methods describedabove.

The optical data in Table 3 illustrates optical stability of the QD filmover a period of time. The EQE of the QD film remained substantiallyunchanged over a period of 24 days under air exposure.

TABLE 3 Example optical data for QD films as a function of exposure toEmission FWHM of Wave-length QD film Time (days) EQE (%) Optical densityof QD film (nm) (nm) 0 48.7 0.084 629 26 3 48.6 0.084 628 25 6 49.80.088 628 25 18 48 0.086 627 25 24 48.7 0.089 627 24

Example Embodiments of a QD Film Based Display Device

FIG. 11 illustrates a schematic of an exploded cross-sectional view of adisplay panel 1100 of a display device, according to an embodiment. Insome embodiments, the display device is an OLED display device or LCDdevice. Display panel 1100 may include a plurality of pixel units 1130,a transmissive cover plate 1132, and a back plate 1134, according to anexample of this embodiment. Even though FIG. 11 shows display panel 1100having few pixel units 1130, a skilled person would understand thatdisplay panel 1100 of a display device may include an one or twodimensional array of pixel units and any number of pixel units withoutdeparting from the general concept of the present invention.

The cover plate 1132 may serve as an optically transparent substrate onwhich other components (e.g., electrode) of the display device may bedisposed and/or may act as an optically transparent protective cover forpixel units 1130. In some embodiments, pixel units 1130 may betri-chromatic having red, green, and blue sub-pixel units. In someembodiments, pixel units 1130 may be monochromatic having either red,green, or blue sub-pixel units. In some embodiments, display panel 1100may have a combination of both tri-chromatic and monochromatic pixelunits 1130. In some embodiments, pixel units 1130 may have two or moresub-pixel units.

Typically, pixel units in display panels have a light source and colorfilters and light emitted from these pixel units are produced by colorfiltering of white light sources to produce red, green, and blue pixelsin a display device. However, the use of color filters is not an energyefficient process as undesired wavelengths, i.e., light energies arefiltered out. Current display devices have used QD films as a color downconversion film in pixel units to reduce the loss of light energy due tofiltering. QDs have a very broad absorption characteristics below theiremission wavelength, and as a result may absorb and convert many of thewavelengths radiating from the light source to the desired wavelength ofthe pixel unit. One of the disadvantages of current QD-based displaydevices is that the high optical density and high QY are not achievedwith thin QD films of few micrometers or less. The QDs tend to aggregateif they are closely packed in thin QD films as discussed above. Suchdisadvantage may be overcome with the use QD films such as QD film 900including barrier layer coated QDs such as QDs 100, 500, 600, and/or900, discussed above, as color down conversion film in pixel units ofdisplay devices.

FIG. 12 illustrates an exploded cross-sectional view of a tri-chromaticpixel unit 1230 of a display panel of a display device, according to anembodiment. In some embodiments, the display device is an OLED displaydevice or LCD device. In an example, pixel unit 1230 may be similar topixel unit 1130 and may be implemented as part of display panel 1100. Inanother example, at least one of the pixel units 1130 may have aconfiguration similar to pixel unit 1230. Pixel unit 1230 may include ared sub-pixel unit 1240, a green sub-pixel unit 1250, and a bluesub-pixel unit 1260. Red sub-pixel unit 1240 may include a white or bluelight source 1242, a QD film 1244 including red-emitting QDs (e.g., QDs100, 500, 600) disposed on an emitting surface of the light source 1242,and an optically transparent substrate 1246. In some embodiments, lightsource 1242 and QD film 1244 are substantially in contact with eachother. As the red-emitting QDs of QD film 1244 may absorb substantiallyall wavelengths (i.e., substantially all light energy) radiating fromthe light source 1242, the use of a red color filter to block outnon-red wavelengths radiating from the light source may be eliminated inred sub-pixel unit 1240, according to an embodiment. In someembodiments, the white light source 1242 is a white OLED or a white LED.The white OLED may include an organic layer configured to emit whitelight.

Green sub-pixel unit 1250 may include a white or blue light source 1252,a QD film 1254 including green-emitting QDs (e.g., QDs 100, 500)disposed on an emitting surface of the light source 1252, and a greencolor filter 1256. In some embodiments, light source 1252 and QD film1254 are substantially in contact with each other and QD film 1254 andfilter 1256 are substantially in contact with each other. Thegreen-emitting QDs of QD film 1254 may absorb substantially allwavelengths smaller and pass substantially all wavelengths higher thantheir emission wavelength radiating from the light source 1252. As such,a green color filter 1256 may be used in green sub-pixel unit 1250 tofilter out the higher wavelengths (e.g., wavelength corresponding to redlight), according to an embodiment. In some embodiments, the white lightsource 1252 is a white OLED or a white LED.

Blue sub-pixel unit 1260 may include a white light source 1262, anoptically transparent substrate 1264 and a blue color filter 1266. Ablue color filter 1266 may be used in blue sub-pixel unit 1260 to filterout wavelengths radiating from the light source that are higher thanblue emission wavelength (e.g., wavelengths corresponding to red and/orgreen light), according to an embodiment. In an embodiment, the whitelight source is a white OLED. In an alternate embodiment, blue sub-pixelunit 1260 may include a UV light source 1262, a QD film 1254 includingblue-emitting QDs (e.g., QDs 100, 500) disposed on an emitting surfaceof the light source 1262, and a blue color filter 1266. In someembodiments, light source 1262 and QD film 1264 are substantially incontact with each other and QD film 1264 and filter 1266 aresubstantially in contact with each other. The blue-emitting QDs of QDfilm 1264 may absorb substantially all wavelengths smaller and passsubstantially all wavelengths higher than their emission wavelengthradiating from the light source 1262. As such, a blue color filter 1266may be used in blue sub-pixel unit 1260 to filter out the higherwavelengths (e.g., wavelengths corresponding to red and/or green light),according to an embodiment. In some embodiments, the UV light source isa UV LED.

The invention also provides a QD-based light emitting diode (LED)comprising a light source unit, a QD film such as QD film 900 comprisinga population of barrier layer coated QDs such as QDs 100, 500, and/or600 disposed on the light source unit, and an optical element disposedon the film layer, according to an embodiment. The light source unit maybe configured to emit light at a primary emission peak wavelengthsmaller than a primary emission peak wavelength emitted by thepopulation of barrier layer coated QDs.

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications of such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

1. A method of making barrier layer coated quantum dots, the methodcomprising: forming a solution of reverse micro-micelles usingsurfactants; incorporating quantum dots into the reverse micro-micelles;individually coating the quantum dots with a barrier layer to formbarrier layer coated quantum dots; and isolating the barrier layercoated quantum dots with the surfactants of the reverse micro-micellesdisposed on the barrier layer.
 2. The method of claim 1, wherein theincorporating of the quantum dots into the reverse micro-micellesincludes forming a first mixture of the quantum dots and the solution ofreverse micelles.
 3. The method of claim 2, wherein the individuallycoating of the quantum dots with a barrier layer includes: forming asecond mixture of a precursor and the first mixture; and forming a thirdmixture of a catalyst and the second mixture.
 4. The method of claim 3,wherein the isolating of the barrier layer coated quantum dots includesheating the third mixture at or below a temperature of about 50° C.under vacuum.
 5. The method of claim 1, wherein the barrier layer coatedquantum dots exhibit a quantum yield greater than about 80%.
 6. Themethod of claim 1, wherein the barrier layer coated quantum dots exhibita quantum yield greater than about 90%.
 7. The method of claim 1,wherein the barrier layer coated quantum dots exhibit a quantum yield ina range of about 85% to about 95%.
 8. The method of claim 1, wherein thequantum dots and the barrier layer coated quantum dots exhibit a quantumyield greater than about 80%.
 9. The method of claim 1, wherein thequantum dots and the barrier layer coated quantum dots exhibit a quantumyield greater than about 85%.
 10. The method of claim 1, wherein thebarrier layer coated quantum dots have an average size ranging fromabout 20 nm and to about 40 nm in diameter.
 11. The method of claim 1,wherein the barrier layer coated quantum dots have an average sizeranging from about 25 nm and to about 35 nm in diameter.
 12. The methodof claim 1, wherein the barrier layer comprises an oxide.
 13. The methodof claim 1, wherein the barrier layer comprises silicon oxide. 14.-38.(canceled)
 39. A method of making barrier layer coated quantum dots, themethod comprising: forming a solution of reverse micro-micelles usingsurfactants; incorporating quantum dots into the reverse micro-micelles;individually coating the quantum dots with a barrier layer to form thebarrier layer coated quantum dots; and performing an acid etch treatmentof the barrier layer coated quantum dots.
 40. The method of claim 39,further comprising isolating the barrier layer coated quantum dots withthe surfactants of the reverse micro-micelles disposed on the barrierlayer after the performing of the acid etch treatment.
 41. The method ofclaim 39, wherein the incorporating of the quantum dots into the reversemicro-micelles comprises forming a first mixture of the quantum dots andthe solution of reverse micelles.
 42. The method of claim 39, whereinthe individually coating of the quantum dots with the barrier layerincludes: forming a second mixture of a precursor and the first mixture;and forming a third mixture of a catalyst and the second mixture. 43.The method of claim 39, wherein the performing of the acid etchtreatment of the barrier layer quantum dots comprises forming a fourthmixture of an acid and the third mixture.
 44. The method of claim 39,wherein the performing of the acid etch treatment of the barrier layerquantum dots comprises: selectively removing the catalyst; and forming afourth mixture of an acid and the third mixture.
 45. The method of claim39, wherein the acid comprises acetic acid, hydrochloric acid, nitricacid, or a fatty acid. 46.-50. (canceled)